The .htaccess file is fine. However, the .htaccess file also includes code to force all traffic to HTTPS. But link.approjectband.com does not support HTTPS yet.
For your main site, you’ve already setup HTTPS, but not for the subdomain. And yes, HTTPS must be setup for every site individually, even for subdomains.
You seem to have some experience already with getting SSL on your site, but here is the guide if you need a reminder: